Two-bands effect on the superconducting fluctuating diamagnetism in MgB&#8322

TL;DR

This study investigates the influence of two superconducting bands on MgB₂'s fluctuating diamagnetism above Tc, revealing a double-structured upturn field linked to two correlation lengths, supported by an extended theoretical model.

Contribution

It provides the first experimental evidence of two-band effects on fluctuating diamagnetism in MgB₂ and extends a recent theory to describe this phenomenon.

Findings

Double structure in the upturn field Hup indicates two correlation lengths.

Diamagnetic response above Tc is consistent with superconducting fluctuations in both bands.

Experimental data aligns with an extended zero-dimensional fluctuation model.

Abstract

The field dependence of the magnetization above the transition temperature Tc in MgB₂ is shown to evidence a diamagnetic contribution consistent with superconducting fluctuations reflecting both the σ and π bands. In particular, the upturn field Hup in the magnetization curve, related to the incipient effect of the magnetic field in quenching the fluctuating pairs, displays a double structure, in correspondence to two correlation lengths. The experimental findings are satisfactorily described by the extension to the diamagnetism of a recent theory for paraconductivity, in the framework of a zero-dimensional model for the fluctuating superconducting droplets above Tc.